This function takes a surface and copies it to a new surface
of the pixel format and colors of the video framebuffer,
suitable for fast blitting onto the display surface. It calls
convert_surface() .
If you want to take advantage of hardware colorkey or alpha blit
acceleration, you should set the colorkey and / or alpha value
before calling this function.
This function can be used to convert a colourkey to an alpha
channel, if the SDL.SRCCOLORKEY flag is set on the surface. The
generated surface will then be transparent (alpha=0) where the
pixels match the colourkey, and opaque (alpha=255) elsewhere.